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8.4.5 density

Paints markers using a configurable colour map to indicate how many points are plotted over each other. Specifically, it colours each pixel according to how many times that pixel has has been covered by one of the markers plotted by the layer in question. To put it another way, it generates a false-colour density map with pixel granularity using a smoothing kernel of the form of the markers plotted by the layer. The upshot is that you can see the plot density of points or other markers plotted.

This is like auto mode, but with more user-configurable options.

Usage:

   shadingN=density colorN=<rrggbb>|red|blue|...
                    densemapN=blacker|whiter|inferno|... denseclipN=<lo>,<hi>
                    denseflipN=true|false densequantN=<number>
                    densefuncN=log|linear|sqrt|square densesubN=<lo>,<hi>

All the parameters listed here affect only the relevant layer, identified by the suffix N.

Example:

   stilts plot2plane layer1=mark in1=dr5qso.fits
                     shading1=density densemap1=viridis
                     x1=psfmag_g-psfmag_r y1=psfmag_u-psfmag_g size1=2
                     xmin=-0.5 xmax=2.5 ymin=-1 ymax=6

Associated parameters are as follows:

colorN = <rrggbb>|red|blue|...       (Color)
The color of plotted data, given by name or as a hexadecimal RGB value.

The standard plotting colour names are red, blue, green, grey, magenta, cyan, orange, pink, yellow, black, light_grey, white. However, many other common colour names (too many to list here) are also understood. The list currently contains those colour names understood by most web browsers, from AliceBlue to YellowGreen, listed e.g. in the Extended color keywords section of the CSS3 standard.

Alternatively, a six-digit hexadecimal number RRGGBB may be supplied, optionally prefixed by "#" or "0x", giving red, green and blue intensities, e.g. "ff00ff", "#ff00ff" or "0xff00ff" for magenta.

[Default: red]

denseclipN = <lo>,<hi>       (Subrange)
Defines a subrange of the colour ramp to be used for Density shading. The value is specified as a (low,high) comma-separated pair of two numbers between 0 and 1.

If the full range 0,1 is used, the whole range of colours specified by the selected shader will be used. But if for instance a value of 0,0.5 is given, only those colours at the left hand end of the ramp will be seen.

If the null (default) value is chosen, a default clip will be used. This generally covers most or all of the range 0-1 but for colour maps which fade to white, a small proportion of the lower end may be excluded, to ensure that all the colours are visually distinguishable from a white background. This default is usually a good idea if the colour map is being used with something like a scatter plot, where markers are plotted against a white background. However, for something like a density map when the whole plotting area is tiled with colours from the map, it may be better to supply the whole range 0,1 explicitly.

denseflipN = true|false       (Boolean)
If true, the colour map on the Density axis will be reversed.

[Default: false]

densefuncN = log|linear|sqrt|square       (Scaling)
Defines the way that values in the Density range are mapped to the selected colour ramp.

The available options are:

[Default: log]

densemapN = blacker|whiter|inferno|...       (Shader)
Color map used for Density axis shading.

A mixed bag of colour ramps are available: blacker, whiter, inferno, magma, plasma, viridis, cubehelix, sron, rainbow, rainbow2, rainbow3, pastel, accent, gnuplot, gnuplot2, specxby, set1, paired, hotcold, rdbu, piyg, brbg, cyan-magenta, red-blue, brg, heat, cold, light, greyscale, colour, standard, bugn, bupu, orrd, pubu, purd, huecl, hue, intensity, rgb_red, rgb_green, rgb_blue, hsv_h, hsv_s, hsv_v, yuv_y, yuv_u, yuv_v, scale_hsv_s, scale_hsv_v, scale_yuv_y. Note: many of these, including rainbow-like ones, are frowned upon by the visualisation community.

[Default: blacker]

densequantN = <number>       (Double)
Allows the colour map used for the Density axis to be quantised. If an integer value N is chosen then the colour map will be viewed as N discrete evenly-spaced levels, so that only N different colours will appear in the plot. This can be used to generate a contour-like effect, and may make it easier to trace the boundaries of regions of interest by eye.

If left blank, the colour map is nominally continuous (though in practice it may be quantised to a medium-sized number like 256).

densesubN = <lo>,<hi>       (Subrange)
Defines a normalised adjustment to the data range of the Density axis. The value may be specified as a comma-separated pair of two numbers, giving the lower and upper bounds of the range of of interest respectively. This sub-range is applied to the data range that would otherwise be used, either automatically calculated or explicitly supplied; zero corresponds to the lower bound and one to the upper.

The default value "0,1" therefore has no effect. The range could be restricted to its lower half with the value 0,0.5.

[Default: 0,1]


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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk